Central and peripheral mechanisms of breathing control in sleeping infants. An investigation of central and peripheral respiratory control mechanisms in normal infants and infants purported to be at 'increased risk' for sudden infant death syndrome.

The integrity of both central and peripheral chemoreceptor function has been questioned in the victims of the sudden infant death syndrome (SIDS). This study describes methods for measuring chemoreceptor function in sleeping infants and their application during the early months of life. It has provided a database of information on normal infants with which to compare results from Infants purported to be at increased risk for SIDS. Central chemoreceptor function was studied in 21 normal infants, 13 siblings of previous SIDS victims and 17 infants who had experienced an apparently life threatening event (ALTE). Peripheral chemoreceptor function was studied in 16 normal infants and 5 siblings of previous SIDS victims. Central chemoreceptor function was assessed using the P 0.1 occlusion technique combined with hyperoxic hypercapnia. The response slope increased exponentially, independent of body weight, over the first 6 months of life. The siblings of previous SIDS victims had a significantly lower slope at any given age than the normal or ALTE infants. A smaller birth weight was associated with a lower slope and during active sleep the slope tended to be lower than in quiet sleep. Although the siblings of SIDS as a group had a lower response to hypercapnia than the normal infants the intragroup variations exceeded the significant intergroup difference so that the technique could not indentify individual infants as belonging to one or other group. Peripheral chemoreceptor function was assessed using equipment specifically designed to deliver a single breath of 100% oxygen to a sleeping infant. The response to the single breath of oxygen expressed as a decrement in ventilation increased with age in absolute terms. This response was consistently larger during mild hypoxia than during normoxia. A lower birth weight was associated with a smaller response. Sleep state did not affect the magnitude of the response. The 5 siblings studied did not differ from the normal infants in their response to the single breath of oxygen. These studies in normal Infants show the development of both central and peripheral chemoreceptor function during the first months of life. Birth weight appears to have a small but significant effect on these responses and this may be important when assessing preterm infants. Siblings of previous SIDS victims as a group have a lower than normal response to hypercapnia; further studies of peripheral chemoreceptor activity are indicated in this group of infants and others in whom risk for SIDS is increased.